The substitution of part of the diesel fuel with natural gas or liquid propane gas [LPG] results in cost savings and improved emissions through better combustion. U.S. Pat. No. 5,224,457 discloses a dual fuel system for a stationary engine. The engine has a diesel injection system controlled by an electronic control unit and a metering valve and mixer which controls introduction of gas into the air intake for the engine. An electronic governor controls the metering valve and a link controller coordinates the ECU and the governor.
U.S. Pat. No. 5,226,396 addresses the problem of varying fuel types and quality of combustion by measuring the oxygen content of the exhaust gases and adjusting the gas supply to the diesel air intake in response to the oxygen content of he exhaust gases. U.S. Pat. No. 6,055,963 discloses a related method in which the oxygen level of exhaust gases as measured is compared to desired exhaust oxygen calculated from engine speed and engine load and then adjusts the energy content value.
U.S. Pat. No. 5,937,800 addresses the problem of varying energy values for added gaseous fuels by establishing a governor out put energy value required and determining energy rates for the diesel and gas fuels as a function of actual and desired engine speed and engine load. U.S. Pat. No. 6,101,986 filed at the same time as U.S. Pat. No. 5,937,800 is concerned with reducing engine speed fluctuations during transition between liquid and dual fuel modes. This is achieved by establishing a desired diesel amount to be added after transition and substituting an amount of diesel with the energy equivalent of gaseous fuel.
U.S. Pat. No. 6,230,683 is concerned with dual fuel PCCI engines and controls the timing of combustion by controlling the amount of gas delivered to the air intake.
U.S. Pat. No. 6,003,478 discloses a dual fuel control system that monitors air intake, diesel intake, exhaust gas temperature and oil pressure. The engine does not shut down when one of the parameters is inadequate but the gas supply can be shut off under no load, low load and excessive load conditions.
U.S. Pat. No. 6,202,601 discloses a system for preventing knocking in a dual fuel engine by monitoring engine load conditions and in high load conditions providing a 3 stage fuel injection. FIG. 1A plots engine load against RPM to determine a flammability limit which is the fuel to air ratio at which the quantity of gaseous fuel will not support stable combustion. In FIG. 1B fuel to air ratios which are considered to be proportional to engine load, are plotted against RPM.
Despite these many attempts gas fumigation of diesel engines has not been widely adopted particularly for automotive engines. The many variables attached to the efficient use of gas in an automotive diesel engine have made it very difficult to devise a practical and economically viable and environmentally advantageous control device.
It is an object of this invention to manage these variables overcome these problems.